1. Field of the Invention
The present invention relates to a heat-resistant adhesive and a method of adhesion by using the adhesive. More particularly, the invention relates to a polyimide-base adhesive which can adhere under mild temperature and pressure conditions, is extremely excellent in adhesion properties and heat resistance in particular, and can be used in the electric and electronics fields, and to a method of adhesion by using the adhesive.
2. Related Art of the Invention
Many heat-resistant adhesives composed of synthetic organic high polymers have conventionally been known as adhesives for various high performance materials used in the fields of electronics, space and aeronautic equipment and transfer machinery. Adhesives which have high heat resistance are polybenzoimidazol-based and polyimide-base adhesives.
Particularly, polyimide-based heat-resistant adhesives which have excellent heat resistance and adhesive strength have been disclosed in U.S. Pat. No. 4,065,345 and Japanese Laid Open Patent Sho 61-143,477. Although these heat-resistant adhesives are excellent in heat resistance and adhesive strength, adhesion must be carried out at high temperature under high pressure in order to obtain high adhesive strength.
When these polyimide-based adhesives are used, a solution of polyamic acid precursor is applied to an adherend surface, subjected to solvent removal and imidization, dried, and adhered to another substrate at high temperature under high pressure. Alternatively, polyimide is processed into films or purified by separating in the form of powder, followed by inserting between the two adherend and adhering at high temperature under high pressure.
Polyimide is a high heat-resistant polymer material obtained by polycondensation of aromatic diamine and aromatic tetracarboxylic dianhydride, and many kinds of polyimide have been known.
Polyimides obtained by using 1,3-bis(3-aminophenoxy)benzene as a diamine component have been known, for example, as follows.
(1) An acetylene radical terminated polyimide oligomer prepared from 1,3-bis(3-aminophenoxy)benzene, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 3-aminophenylacetylene (N. Bilow et al. U.S. Pat. Nos. 3,845,018 and 3,879,349).
(2) A polyimide prepared by polycondensation of 1,3-bis(3-aminophenoxy)benzene and pyromellitic (T. P. Gannett et al., U.S. Pat. No. 4,485,140).
(3) Heat resistant adhesives prepared from 1,3-bis(3-aminophenoxy) benzene and various kinds of tetracarboxylic dianhydrides (Japanese Laid-Open Patent Sho 61-143,477 and 61-291,670).
(1) is an addition type thermosetting polyimide in which the oligomer end is blocked with a 3-aminophenylacetylene radical and the terminal acetylene radical is involved in a cross-linking reaction by heat treatment.
(2) is a condensation type polyimide obtained by using 1,3-bis(3-aminophenoxy)benzene as a raw material monomer and characterized by using pyromellitic dianhydride as a tetracarboxylic dianhydride component.
(3) are heat resistant adhesives composed of 1,3-bis(3-aminophenoxy)benzene and various kinds of tetracarboxylic dianhydrides. However, a reactive radical remains at the end of polymer chain and severe conditions such as high temperature and high pressure are required in order to obtain heat resistant adhesion.